Correcting maps

I have some fields that are not the right shape (partial 1/4s) that I would like to correct. Can you point me to a FAQ or describe how to do it? One is a square 40 that shows up as rectangular. I own the other 3 forties in that 1/4 and cash rent the one I want to correct. Seems like I need to delete the fields and re draw them. Is that right?